The present invention relates generally to foundry molds for use in casting metal shapes.
It is an object of the present invention to provide a new composition that is particularly well adapted to the fabrication of molding elements. A more particular object of the invention is to provide a material for molds comprising selected amounts of vitreous fused silica.
At the present time, foundry casting commonly utilizes metal molds, generally of an all metal, unitary construction. The use of most metals presents numerous disadvantages.
The very high thermal conductivity of these prior metal molds is probably the biggest disadvantage. In addition, the chemical elements in the metal molds present the risk of migrating in the cast piece during molding; this is notably due to the difference in chemical potential that can exist between the mold and the material to be shaped.
Some of these problems are solved by the use of a lubricant or release agent, in which a coating is applied inside the metal molds. However, due to the stresses exerted on the walls of the mold, this release agent does not solve the above problems in a permanent manner and is only a temporary measure. In addition, applying a lubricant or release agent is a time consuming operation that immobilizes the molds. This necessitates having at least two sets of molds, one having the lubricant applied while the other is in service. Furthermore, the whole set of equipment is immobilized when one set of molds is replaced with another. In this latter case, a loss of productivity on the order of 10%-20% is relatively common.
Among the various problems that remain unresolved, those induced by the excessively high thermal conductivity of the molds are the most important. In particular, the fact that there are zones of variable thickness in the piece to be molded leads to difficulties in filling the mold, with the narrowest parts cooling much more rapidly. In order to remedy these difficulties, one is generally forced to (1) provide a substantial volume in the feeder heads, which serve as a reserve for the piece to be molded and (2) to heat the molds before and frequently during production and (3) to increase the temperature of the molten metal material feeding the mold.
All these remedying measures are very costly in both money and energy.
Accordingly, one object of the present invention is to provide a material that can be used for the molds, but does not chemically react with the materials to be shaped.
Another object of the present invention is to provide a mold material whose thermal conductivity can be selectively controlled.
Another object of the present invention is to provide a material of the above type that does not require a release agent.
Another object, finally, is to provide molds or parts of molds produced of this material.